1. Field of the Invention
The present invention relates to a semiconductor device, and particularly to a semiconductor device that is applicable to an SOI (Silicon On Insulator) structure, and to a manufacturing method thereof.
2. Description of the Related Art
A transistor having a plurality of conductive channels has been known as a minute transistor having a high driving ability. For example, in Japanese Unexamined Patent Application Publication No. 2001-298194, a transistor in which a plurality of conductor channels consisting of semiconductors are arranged in a given direction on an insulator is shown. In the transistor, a plurality of semiconductor layers that form conductive channels (channel regions) are arranged at intervals in a given direction. Each of the semiconductor layers has a rectangle cross section. According to the transistor, a double gate structure is obtained by forming a gate electrode at both sides of each semiconductor layer, which is expected to lead to a high driving ability. However, in the transistor, because the cross section of semiconductor layers forming conductive channels is rectangle, there is a tendency that a gate insulator is damaged due to the concentration of electric fields, which is caused by a partly thinned gate insulating layer at its corner. Also, in the transistor, because channel surface directions change at every corner, changes in the characteristics of the gate insulating layer occur. These changes may considerably affect the reliability of the transistor.
The present invention is intended to provide a minute semiconductor device having a high driving ability and a manufacturing method thereof.